The Law of Thermodynamics
by Ghost4
Summary: Oneshot: Castiel and Sam have a chat. If you have read *any* of my ‘chat’ fics, then you know: H/C Tag for “The Song Remains the Same”. Companion piece to Mikiya’s “Thank You”. Mikiya2200


Title: The Law of Thermodynamics

Author: Ghost4

Rating: Feels weird to call any of my fics K+, but this probably is. Going with T anyway.

Disclaimer: I don't own them. Really. I know, shocking, isn't it?

Author's Note: I do not like Cas. I do not like the angels on SN at all. Imagine my surprise when Castiel started talking to me. We have reached a friendly ceasefire for now. ;)

Companion piece to Mikiya's "Thank You" (Mikiya2200 here at FFN or http:// mikiya2200(dot)livejournal (dot)com/ ) Thanks you, Miki, for the help in finding Cas, and in the beta. All remaining mistakes are all about me.

As always: Any responses, good, bad, or indifferent, are very welcome.

* * *

Castiel woke and opened his eyes in the very same instant.

He knew where he was – Dean's motel room. He remembered the pain of his return, falling into the brothers' waiting arms. It was almost the same reception he would have once expected from his angelic siblings, the instant support, the compassion, the lack of judgment.

It had been far too long since he'd felt that kind of acceptance among his own kind. Maybe it was a sign of how far he had fallen that it was only among humans that he could feel…almost at home.

But the simple truth was that he had no home any longer.

Castiel sat up – and listed as the whole of existence turned uneasily in his borrowed skull. For a moment he felt himself slipping, his grace trying to fling itself free of its fleshy prison – and he wanted to free it. He wanted to free himself from the bounds of this dirty, slow existence. But to do so would be suicide. The Host would be after him, after Dean and Sam Winchester, before he could even begin to stretch his 'wings'. But he just couldn't care at the moment. He hurt, the pain like a cramping muscle inside him, one that only extending himself would relive. He needed to hear from Heaven again. He needed to feel his family's love again. He needed. So _much_.

And that _need_ was repugnant. Shameful.

He was an abomination.

He shouldn't continue.

He felt his borrowed flesh giving in, giving way. The pain engulfing him like the fires of Hell… or of Heaven's grace.

Hands grabbed him, steadied him, grounded him… and he swallowed, relaxing into the hold and letting his brother support him.

Except that it wasn't his brother. It couldn't be. He was tainted now, unclean and unsafe and his brothers had turned on him and cast him out.

The arms tightened around him as he shuddered with the agony of that separation again. He allowed himself to be clutched close, to be cosseted, because he was so separate here, so cut off from everyone and everything that had ever mattered to him.

Cut off from everything that had ever mattered… until it was wrong. Until it felt… aberrant and unsafe and _unintended_. And then all that had mattered was finding his Father and finding out what he was supposed to do about it all.

And being alone in that need.

Castiel reached up, grabbing at the arms that held him compulsively in reaction to the stark fear that being alone brought. He was not alone. He was not alone. He may have been cast aside by his family, but he was not alone.

The thought – and the presence of the steady, supporting arms – calmed him. Slowly he reeled his glory back into place, he fought himself back into this dull, hurting shell.

He could do this. He was not alone.

Castiel sighed, opening his borrowed eyes. "Thank you," he murmured quietly to the man behind him, holding him through the tremors that had shook the body. Castiel knew it couldn't have been pleasant – the glory seeping from him would have burned like soft lightening.

"Thank you, Dean," he said again, feeling himself become sealed into the flesh once more.

"Are you okay now?"

The voice was hesitant, hiding pain… and not Dean Winchester.

Castiel jerked free of the supporting arms. "Sam."

Instantly the man let go, shifting away from him. "I'm sorry," Samuel said, standing and taking the few short steps away that the room allowed. "I wouldn't have… wouldn't have gotten into your space, but you looked like you needed help…"

The words, hesitant and almost embarrassed, drifted off. Samuel's eyes drifted as well, falling to the carpet. He crossed his arms, and rubbed roughly at his skin. He was wearing short sleeves and Castiel could see the red irritation that would have come from holding his body – holding _him_ – as his grace attempted to burst forth.

Sam had caused himself pain in order to offer him comfort.

Castiel felt something hard and painful take root in his throat at the thought. He swallowed past it, trying to decide how to respond. He had no experience for this kind of situation. A member of the Host, they might make such a sacrifice for one another… but a human?

He was continually amazed by both the wondrous kindness and shattering misery this species could practice. Before, it had been almost an academic exercise. He had watched as they healed and hurt one another in almost equal measure, the chaos of it all confusing and disgusting him. Now though….

Now he was a part of that chaos. Now he was intimately involved with the pain and joy of the human experience.

And hadn't he caused some of that chaos himself? Hadn't he brought just that into the life of the man standing so unsure before him?

Castiel's blood heated uncomfortably. There was a truth there, as hard and sharp as any sword that could slaughter an angel.

He had brought pain into this man's life.

He had only been following orders.

But he had brought needless _pain_ into this man's life.

The man who was standing there, head hanging and shifting nervously, waiting to be judged and found wanting.

Castiel didn't know if he could do this; if he could be here with a person who he owed such a debt, to whom he had caused such great harm. "Where is Dean?" he asked, just for a way to shift his attention from Samuel.

"He went to get some food," Samuel said almost apologetically. "He should be back soon, and you were out. We figured it would be okay." He took another, truncated step back and leaned against the wall.

Putting as much distance between them as possible. "'Be okay?'" Castiel repeated, not understanding.

Samuel shrugged, the oddly human movement looking both resigned and somehow tired. "I – we know you really aren't that comfortable with me. But you were sleeping so deeply that Dean was sure he'd be back before you came to."

"That I am not comfortable with you…" it was half question. And then Castiel slowly realized Samuel had backed away not for his own comfort, but for Castiel's.

Sam shifted again, trying to look unconcerned. "Yeah. It's okay. I get it. Your kind tend not to like… me."

Castiel didn't insult Sam by pretending he didn't know what the human intended by the words. "Your blood."

Sam nodded, a hard, almost jerky movement. "My blood."

Castiel had no response. In fact he wasn't entirely sure a response was required. The blood was the truth of Sam, much like the grace was the truth of his own existence. He could change neither.

No matter how much he might desire it at times.

Samuel was watching him, however. There was an expression on his face – almost expectant, but not completely so. Castiel sat back down on the bed. He felt a desire to sleep, a desire to leave and find Dean – or just to leave. Be…away from this human existence for a time.

But he owed both Dean and Sam too much to leave them without good reason. And he was still weak.

He looked up at the man across the room. Sam had lowered his arms, tucking his hands behind his back. His forearms were beginning to turn bright red, as if he was developing a solar burn. In a way, he was. It would heal, but not without pain. Not that Castiel could help with that either… not anymore.

He was obviously waiting for something.

"What is it that you want?" Castiel found himself asking. "Should I have responded?"

Samuel's jaw clenched, but he shook his head. "No. I mean, what is there to say? It's fact. It's who I am."

It was truth, but Castiel was surprised by the way something in his chest ached at the confession. "That is not completely accurate," he found himself arguing. "It is part of you, yes; but it is not who you are. Or who you need be."

Sam's mouth twisted in a bitter smile. "Maybe, maybe not. But it was enough to send Anna back in time to kill me… to kill us."

For the first time, Castiel found himself needing to speak, needing to comfort. "They do not know you, Sam. Not as an individual. They see your blood, your taint, and on this alone, they judge you."

"Maybe they should," the man said, leaning forward slightly. His eyes were bright and hard and there was a need in him Castiel could almost feel. Something alone and separated from his family, from his kind. Something Castiel recognized. Something expectant.

"What is it you desire to know, Sam?" Castiel asked.

Samuel's eyes closed for just a moment, whether in pain or prayer, Castiel couldn't tell. For Samuel, they were often the same anymore. But when they opened, Castiel met a clear and somehow intense gaze.

"What Anna said she could do, kill me and scatter me enough that Lucifer couldn't put me back together – can you do that? Can you…destroy me like that? Make sure I can't come back?"

Castiel felt the wince more in his chest then in the flesh. "You would do that? You would die in that way, leaving nothing behind? Truly?"

"Yes."

One word. And a lifetime of pain and loss and the fear of causing more. It was spoken without hesitation, without pause. It was only one human lifetime, and a short span at that, but the ache in the word belied the limited days and turned agony into an eternity.

Castiel's stomach clenched. "What about what it would do to Dean?"

Samuel's hard resolve crumbled. He fell – not physically, but Castiel could see the fall in him clearly, in the slump to his shoulders, the cast of his eyes. "I love Dean. He's all I have left. But I'm hurting him, Cas. My just being here hurts him. I was supposed to die back on that road in Cold Oaks. I was supposed to die _human_. Now…" he stopped, turning his head to the side and swallowing. When he looked back Castiel could see the faint shaking of his body from across the room. "Now, I'm just a monster."

The man was so tired. So very weary. Heart-sick and broken in so many, many ways.

He had taken in demonic blood. He had killed. He had willingly followed the advice of Hell.

He had also been denied every choice he had made for himself and his own life. He had lost to evil every single person who had ever touched his heart. He had been betrayed by Heaven.

And he stood there, slumped against a moldy wall, arms blistering from an act of kindness toward one who had not earned it – and he called himself a monster.

"You are no monster, Sam," Castiel said, sure of the words for the first time. "There was once I would have called you such. When I told Dean that you were a creature to be hunted. I know now how false that was. You are human; as flawed and brave and strong as any of your kind. You are no monster to be killed and forgotten."

"I have demon blood," Samuel reminded him, merciless as any of the Host. "Enough of it that you can barely stand to be near me. What does that make me if not a monster, Cas?"

It was always surprising, what these creatures could miss. So clever, so very clever, yet so strangely limited. "I do not keep my distance from you because of the demon blood, Sam," Castiel assured him.

Samuel's expression turned bitter. "No, because it's even deeper then that, isn't it. I was flawed from the beginning."

Castiel's head was aching. "I have no idea what you mean," he said wearily. "I don't often understand human reasoning."

"Dean met with Michael, Castiel," Samuel said.

The angel felt a strange ache ripple though him – one made of both fear of the most powerful archangel, and longing for him. "Dean saw Michael?"

Samuel nodded. "Saw him, and spoke to him. Michael told Dean about the bloodline. About how he can be a vessel because he carries the blood of Abel and Cain. The first human brothers." Sam looked pale. The fresh burns on his arms stood out in bright contrast. The shaking had increased. "And if Dean is Abel…I think we all know who I'm meant to be. I don't want to kill Dean, Cas. And if you can stop it, stop _me_…please."

He was begging. Begging for his own death… for more then his death, for his complete destruction. There would be no afterlife, no rest – just…eternal void.

Castiel wanted to weep for it. "You don't understand, Sam."

"I do," the man argued earnestly. "I know that I'll be completely gone. I know that there can be no coming back. I don't care."

"No, it's not that. You don't understand the bloodline, Sam." Castiel took a breath, it was so difficult trying to explain the very simplest of concepts to these creatures. They had never joined with the Host, had never felt the Divine in a single seed, let alone seen it shining bright and fearsome from the forest. How could you explain anything to a creature so…abridged?

"The bloodline," Castiel continued, before he could get lost in what he had given up to follow his own path, before the loneliness could swallow him. "The bloodline is not one or the other. It stands before them, between them. It is… _family_."

"Family?"

Castiel fought to find the words to explain. "Cain and Abel. They were of the first of your kind. Part of the few who ever saw God in person. The encounter left them with a touch of grace."

Samuel's eyes widened. "The same grace as Anna? As you?"

Castiel nodded, relieved at his easy understanding. "Yes. The same. Just a touch, you understand… but no creature comes away from the Divine without being touched in some way. That grace survived in their bloodline, in their descendants – spreading to a handful of people born around the world."

"People born able to become the vessel for angels," Samuel extrapolated, watching Castiel closely, not trusting… but reluctantly believing despite everything.

"Yes, because they hold a spark of Divine grace. They can survive the power of the angel's grace because it is _of_ them, even if just a slight trace."

Samuel shook his head. "But Cain killed his brother." It was obvious from the tone that Samuel could not conceive of a greater sin. "How could he have even a touch of grace?"

"The grace exists regardless of acts. It can not be extinguished."

"That's why Anna had to hide her grace. Even torn from her, it still existed. She couldn't destroy it," Samuel sounded… calm. Thoughtful. He was happiest when solving mysteries.

And he was good at it. "Yes," Castiel confirmed. "Grace exists. It _is_."

A strange smile twisted Samuel's face. "First law of thermodynamics: energy can never be created or destroyed."

"I don't know what that means," Castiel admitted.

Samuel shrugged. "It doesn't matter. So the… touch of grace – it got passed down?"

"Through the long history of man… until it didn't matter any more. Until it was forgotten by all …save one." And perhaps that had been the greatest mistake; that they, the angels, had forgotten the touch of grace in mankind… but Azazel had not.

"And Dean inherited it from Dad," Samuel finished.

Castiel nodded. "He did – as did you, Sam."

The human froze. He locked – his heart hesitated in its rhythm, even his aura stilled for a moment. Then he spoke, the words slow but sure. "No. Dean inherited the bloodline. Dean inherited the touch of grace. _Dean_. Not me."

It was not an argument. It was stated, calm and rational and reasoned. He wasn't fighting, he was correcting.

And he was wrong.

Castiel shook his head. It was unlike Samuel to misunderstand something simple. "No, Sam. Dean and you both inherited the trace of grace."

Samuel stared at him for a long silent moment. Emotions flickered behind his eyes, so fast and so many that Castiel had no chance to interpret. His hands fisted and relaxed twice at his sides. When he spoke, it was a single word that felt like a scar.

"How?"

Castiel blinked, surprised by the question. "You share the same father, Sam. You and Dean share the same bloodline."

Samuel was shaking his head though, obviously upset. "No. It can't be the same. I'm… It can't be the same, Cas!"

And then he understood. And he ached for the tormented soul across from him. "It is the same bloodline, Sam. From John, to you and Dean both. Both of you were born with the trace of grace in you." And Castiel paused, trying hard to meet Sam's haunted and confused eyes. "It was what drew Azazel to your family. It is what drew him to all the families he ruined."

Sam shuddered, as massively and painfully as Castiel had only minuets before. But where Castiel had been fighting to contain his glory, Samuel was struggling to control his hurt. Sam stood alone, his arms crossed over his chest, holding himself together without anyone to support him.

Samuel was as brotherless as he was, now.

"Wha-" Samuel tried, but his throat seized. He cleared it and tried again. "Why?"

"He saw an opportunity. A vulnerability that we had forgotten. For Lucifer was an angel, not a demon. As an angel, he would need a host who bore the trace – anyone else would not be able to hold the grace of a former archangel. But Lucifer's grace had been…twisted. It could not be destroyed, but it was changed. Do you understand?"

Sam laughed brokenly. "The second law of thermodynamics: energy can be changed from one state to another."

Castiel frowned. "I do not know what that means."

Samuel slid down the wall, sitting in a loose knot. He was staring blankly at the ceiling. He was still shaking. "It means I understand." His voice was dull.

Castiel didn't know how to respond. So he continued. "Azazel had been told that the person who could be Lucifer's vessel must be one of the bloodline… but one in whom the blood had been altered. The trace becoming a taint." Castiel felt the muscles behind his shoulders tighten. "I have come close to loosing my grace before. I know the pain, the agony, of even loosing control of it for a moment. To have it changed in such a way – to have innocence and purity torn away and twisted inside you…I can not imagine the pain you experienced, Samuel. That you have experienced every day since. That you held against that pain for so long…" Castiel closed his eyes. "It humbles me, Samuel. And it saddens me. I wish –"

"If wishes were horses, beggars would ride." Sam said, cutting him off heartlessly. His voice never lost its lifelessness. Then his head came down, and for a brief moment Castiel saw the long, chronic ache of that old wound in his eyes – and the angel's heart twisted in sympathy.

Then Samuel's eyes shuttered again, hiding that infection away once more. "Why me?" he asked. "If we were both born with the trace of glory, why did the yellow-eyed bastard pick me?"

"Chance," Castiel answered. "Only chance, Sam. When he saw that John intended to take Mary to wife – he knew the bloodline would be passed on. He engendered the deal for access to John's children through Mary. He did not really care which child he tainted. Had you been born first…"

"It could have been Dean," and there was real fear in Samuel's eyes now. "Oh, my god. It could have been Dean."

Castiel nodded slowly. "Had you been born at different times, you would have switched places in every way. You are not inherently evil, Sam. That it was you, and not Dean, was sheer chance."

Sam looked at him, eyes raw and wet, huddled on the floor, and Castiel wanted to go to him, wanted to offer the same kind of comfort that Sam had offered him. But he didn't know how.

Sam was human. Castiel was … not.

They both flinched as the door knob rattled. Instinctively Castiel looked back at Samuel, who was getting to his feet, rubbing a rough, burnt hand over his face, obliterating all traces of the tears and pain that had marked his skin.

"Sam," Castiel started, not sure what he would say, but wanted to express some kind of… sympathy, or support…or regret.

Samuel's eyes were once again hard as they flashed up, however. "Don't," he warned desperately. "Don't do that. And don't ever tell Dean any of this. Don't ever tell him that it could have been him. It could _never_ have been him, understand?"

And Castiel did. Dean did not need that burden on top of everything else he carried. He nodded his understanding at Samuel as the door opened.

Dean stepped through, juggling a couple of bags that smelled like burnt, rancid meat. "Hey, Sam," he started, then looked up. "Cas! Hey! You're up. Good. You feel better?" Dean sat the bags down on the table.

"I am fine, Dean," Castiel assured him.

"Good, because I've been – what the hell?" The last was muttered as his eyes finally touched on Samuel, standing in his corner. "What happened?"

Samuel shrugged, an almost embarrassed smile flickering around his mouth. "Nothing. Cas had a bit of a rough spot. Got a little glowy. But he got it under control."

Dean frowned, taking in Sam's disheveled look and the burns which were quickly blistering. Castiel stood still as he turned those assessing eyes his way. "You okay?"

"I am fine," the angel repeated.

Dean looked between them again. "Is there anything I need to know about here?"

Castiel could not help looking at Samuel. There was so much Dean should know. So much Dean should understand – about his brother and his bloodline and the crimes of Heaven and Hell.

But it was knowledge that would only bring pain and self doubt, and was is nothing that he _needed_ to know.

It was Samuel who spoke. "No, Dean. Really. It was just Cas hurting a bit before he woke up."

"Cas?" Dean asks, not bothering to hide his distrustful look.

He did not see the way Samuel flinched from the implied judgment. Samuel, who would go so far to ease his brother's burden, to save him from pain… and Dean did not even see the pain he so casually inflected as he strove to achieve his purpose.

Dean was becoming ever more angelic. Sam was only human.

"No, Dean," Castiel found himself replying. "There is nothing you need to know right now." Because it was not the time to weaken Dean, or distract him.

And he saw Samuel, alone, cut asunder from his brother.

And his heart wept for all three of them.

~end


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